Most of my Izotope plug-ins are unusable because the windows are chopped off, like this one:
Not just chopped off, but the x/y reference seems to be out of sync. In this case, I can fly over a section , which exposes the Solo button, but I can’t click on the button. I think that is because the plug-in thinks I am at a different x/y location than Cubase does.
Supposedly the pull-down menu should have an option to allow the window to be re-sized, but I see nothing like that in the pull-down. It looks like there is a resizing handle at the lower right, but it is not responsive, probably because of that x/y confusion I mentioned above.
Any ideas how to get this working?
I just used the resizing handle on the lower right. This is the smallest I can get it:
It never does any truncation, no matter what proportions I attempt to use on the overall window size. I’m not finding any other way to resize it. FWIW, the version information on my copy shows v2.10.0.984 WIN64.VST3. I am using Windows 11, and the resolution of both of my monitors is 1920x1080.
A resizable GUI does seem to be on the high priority list, for years… 
I played around some more, and sometimes I could use the resizing handle, but it was really tedious. I have 3 monitors. The only way I could grab the sizing handle was to drag the TBC window onto my smallest, leftmost monitor, actually spanning 2 monitors. Then I could grab the handle. Once I stretched it a little, I could then drag the window anywhere and use the handle. I opened this under StudioOne and it behaved similarly. So I guess it is working the way Izotope expects it to.
I’m not sure this plug-in is really very useful, so I guess it is no big loss.
I’ve seen some other threads about current Cubase 15 bugs relating to multiple monitors with different sizes. I don’t know if that may be applicable here since it is a third-party plugin, rather than something built into Cubase, but you may want to check around for threads on that subject to see if they may describe similar symptoms. (My monitors are both identical, and I have not experienced any issues.) I think I also saw something suggesting the issues in that area were going to be fixed in the first main maintenance release. (15.0.6 didn’t count as it was meant for some specific high-priority issues.)
I doubt iZotope expects that, but, if it is happening with multiple DAWs, perhaps it is an iZotope-specific issue, in which case reporting the issue to iZotope’s support would probably be a good idea.